Car spark plug carbon deposits are a problem that many car owners will encounter. Spark plug carbon deposits can cause engine shaking, power loss, increased fuel consumption, and even difficulty starting. So, how to deal with spark plug carbon deposits? How to prevent it?
Poor quality fuel: contains too much impurities or colloids, incomplete combustion, and residues attached to the spark plugs.
Improper fuel additives: Some additives may increase the formation of deposits.
Octane mismatch: Low-grade fuel is prone to detonation in high-compression ratio engines, resulting in abnormal combustion.
Too rich mixture (too low air-fuel ratio):
Excessive fuel injection (such as injector leakage, oxygen sensor failure).
Air filter blockage leads to insufficient intake.
Incomplete combustion, producing free carbon particles.
Too lean mixture (too high air-fuel ratio):
May cause excessive combustion temperature and partial incomplete combustion.
Insufficient ignition energy:
Aging spark plugs, ignition coil failure or high-voltage wire leakage lead to weak sparks and inability to fully burn fuel.
Ignition timing deviation: Ignition too early or too late affects combustion efficiency.
Long-term idling or short-distance low-speed driving:
The engine temperature is low, the fuel is not completely volatilized, and carbon deposits are easily formed.
Burning oil:
The piston ring/valve oil seal is worn, and the oil seeps into the combustion chamber, and ash-like carbon deposits (white or gray-black in color) are produced after combustion.
Insufficient cylinder pressure:
Wear of the piston ring leads to a decrease in compression ratio and incomplete combustion.
Mismatched calorific value:
Cold spark plugs (fast heat dissipation) have insufficient temperature when running at low loads and are prone to carbon deposits;
Hot spark plugs (slow heat dissipation) may overheat under high loads, but carbon deposits will also occur if they run at low temperatures for a long time.
Abnormal electrode gap: Too large or too small affects the ignition effect.
Turbocharged engine: High temperature and high pressure environment is more prone to carbon deposition.
EGR valve failure: Excessive exhaust gas recirculation, lower combustion temperature, and increase carbon deposition.
Long-term use of inferior engine oil: The residue increases after the engine oil vapor participates in combustion.
Steps:
Remove the spark plug:
After the engine cools down, disconnect the ignition coil or high-voltage wire, and use a special spark plug wrench to unscrew the spark plug.
Observe the electrode and insulator:
Normal state: The electrode is light brown or grayish white, and there is no obvious deposit on the skirt of the insulator.
Carbon deposition performance:
Black dry carbon layer: The electrode and insulator are covered with black velvety or granular carbon deposition (the mixture is too rich or the combustion is incomplete).
Oily black dirt: accompanied by sticky oil stains (may burn engine oil).
White or grayish white deposition: may be fuel additive residue or engine oil ash.
The following symptoms may indicate spark plug carbon deposits:
Cold start difficulties: Carbon deposits affect ignition energy, resulting in ignition failure when the vehicle is cold.
Idle speed jitter: Some cylinders misfire due to spark plug carbon deposits, and the engine speed is unstable.
Weak acceleration/frustration: Ignition efficiency decreases under high load, and power output is inconsistent.
Increased fuel consumption: Combustion efficiency decreases, and the ECU may increase the injection amount to compensate.
Exhaust odor: Unburned fuel is discharged, and the exhaust has a pungent gasoline smell.
Cylinder cut-off test:
When the engine is idling, unplug the ignition coil or high-voltage wire of each cylinder in turn.
If the engine jitter does not change significantly after a cylinder is cut off, it means that the cylinder is working abnormally (the spark plug may be carbonized or damaged). (Note: This method is not suitable for direct injection engines or some sensitive models, and may trigger fault codes)
OBD diagnostic instrument detection:
Read engine fault codes.
Check the long-term fuel correction value (negative value may be too rich mixture leading to carbon deposits).
|
Appearance of carbon deposits |
Possible causes |
|
Dry black carbon powder |
Too rich mixture, long-term short-distance driving |
|
Wet black oil stains |
Burning oil (piston ring/valve oil seal problem) |
|
White or grayish white deposits |
Fuel additive residue or oil ash |
|
Red or rusty deposits |
Iron additives in the fuel (rare) |
Heat value matching: When replacing spark plugs, you need to select the correct heat value (refer to the vehicle manual), otherwise it may aggravate carbon deposits.
Joint inspection: If carbon deposits are serious, check whether the fuel injector, oxygen sensor, EGR valve and other components are faulty.
Cleaning and replacement:
Mild carbon deposits can be reused after cleaning with a special cleaning agent or ultrasonic cleaning.
Severe carbon deposits or electrode wear require direct replacement.
Steps:
Remove the spark plug and use a wire brush or an old toothbrush to initially remove large carbon deposits on the surface.
Soak the spark plug in a special cleaner (such as carburetor cleaner, spark plug carbon deposit remover) for 10-15 minutes.
Use a fine needle or toothpick to clean the residual carbon stains in the electrode gap and wipe it dry with a soft cloth.
After drying, check the electrode gap (refer to the vehicle manual, usually 0.7-1.2mm), and adjust if necessary.
Note:
Strong acid and alkali cleaners are prohibited, which may corrode metal or ceramic insulators.
After cleaning, dry thoroughly to avoid short circuits.
Steps:
Mix white vinegar and baking soda (ratio 2:1) into a paste and apply it to the spark plug electrode and thread.
After standing for 30 minutes, brush it lightly with a toothbrush, rinse with clean water and dry it. (The effect is weak, only suitable for slight carbon deposits)
Steps:
Put the spark plug into an ultrasonic cleaner and add cleaning fluid (special solvent or diesel).
Use ultrasonic vibration for 10-20 minutes, and the carbon layer will fall off.
After taking it out, use compressed air to blow dry the electrode gap.
Advantages: It does not damage the electrode and can clean stubborn carbon deposits.
Steps:
Use fine sandpaper above 600# to lightly grind the electrode surface, or use a copper wire brush (steel brush is prohibited, which may scratch).
Blow away the debris after cleaning to avoid metal particles remaining.
Note:
Use platinum/iridium spark plugs with caution, which may damage the precious metal coating.
The electrode gap may change due to grinding and needs to be readjusted.
Keep the engine running at 3000-4000 rpm for 10 minutes on a safe road section. The high temperature can partially burn away the carbon deposits.
Suitable for slight carbon deposits, the effect is limited.
Use quartz sand to spray the surface of the spark plug at high speed to completely remove stubborn carbon deposits.
Requires professional equipment, and self-operation may damage the spark plug.
Check the status of the spark plug:
No deformation of the electrode and no cracks in the insulator.
Severe ablation or excessive gap (more than 1.3mm) requires direct replacement.
Installation points:
Apply a small amount of anti-seizing agent to the thread (to avoid difficulty in disassembly next time).
Tighten according to the standard torque (usually 20-30N·m, refer to the manual).
Use high-quality fuel
Choose regular gas stations (such as Sinopec and PetroChina) to avoid impurities and colloids in inferior fuel.
For turbocharged or high-compression engines, it is recommended to use gasoline with a grade of 95# or above to reduce the risk of knocking.
Add fuel additives regularly
Use a fuel saver containing PEA (polyetheramine) every 5,000-10,000 kilometers to clean the injector nozzle and carbon deposits in the combustion chamber (such as Chevron TCP and Red Line SI-1).
Note: Direct injection engines need to choose "direct injection-specific" additives.
Avoid long-term low-speed/short-distance driving
When the engine runs at low temperatures, the combustion is not complete and carbon deposits are easy to form.
Solution: Drive at medium and high speeds (above 80km/h) for 20 minutes at least once a week to increase the combustion chamber temperature.
Reduce idling time
Long-term idling (such as waiting for people or in traffic jams) will cause the mixture to be too rich and increase carbon deposits.
Suggestion: Turn off the engine when parking for more than 3 minutes.
Repair the burning oil problem in time
Burning oil will form oily carbon deposits on the spark plug.
Checkpoints:
Blue smoke from exhaust.
Abnormal oil consumption (consumption > 0.5L every 5,000 kilometers requires inspection).
Replace the air filter regularly
Blockage will lead to insufficient intake volume and too rich mixture (it is recommended to replace every 10,000-20,000 kilometers).
Clean the throttle and intake duct
Disassemble and clean the throttle every 30,000 kilometers to reduce the accumulation of sludge affecting the air-fuel ratio.
Check the EGR valve
The EGR valve will cause excessive exhaust gas circulation, reduce the combustion temperature, and increase carbon deposits.
Performance:
The center electrode becomes round and the side electrode is concave (normally it should be a square edge).
The electrode gap exceeds 1.3mm (the standard is usually 0.7-1.1mm, which needs to be measured with a feeler gauge).
Consequence: Insufficient ignition energy, resulting in misfire and reduced power.
Cause: Thermal stress shock or excessive torque during installation.
Risk: It may cause high-voltage leakage and cause engine shaking.
Performance:
The electrodes and insulators are wrapped in thick carbon deposits (black sludge or dry carbon), and the ignition is still poor after cleaning.
Accompanied by idle shaking and cold start difficulties.
Characteristics: There are oil stains on the spark plug threads or electrodes (oil seeps into the combustion chamber).
Root cause: It is necessary to check whether the piston rings and valve oil seals are aging at the same time.
OBD detects P0300 (random misfire) or P030X (misfire in cylinder X), and eliminates ignition coil fault.
Acceleration is weak, fuel consumption increases by more than 10%, and there is no improvement after cleaning the spark plug.
Long-term short-distance/low-speed driving:
Frequent cold starts are prone to carbon deposition, and it is recommended to shorten the cycle by 30% (such as replacing iridium spark plugs after 60,000-70,000 kilometers).
Modification or high-load driving:
After flashing the ECU and increasing the boost value, the spark plugs are subjected to higher temperatures and need to be replaced with higher specifications.
Using ethanol gasoline:
Ethanol gasoline above E10 has a high combustion temperature and may corrode the electrodes. It is recommended to replace it 10,000 kilometers in advance.
Disassembly and inspection
Normal state: the electrode is light brown and the insulator has no cracks.
Abnormal state: electrode ablation, carbon deposits, oil stains, whitening (overheating) or rust.
Multimeter measurement
The resistance value exceeds the manufacturer's standard (usually 4-8kΩ), indicating aging.
Repair shop inspection
Cylinder pressure test + ignition waveform analysis to accurately judge the working condition of the spark plug.
The spark plug is responsible for generating electric sparks in the combustion chamber, igniting the mixture, and driving the piston to move. It is a key component for the normal operation of the engine.
Symptoms: difficult cold start, idle jitter, weak acceleration, and increased fuel consumption.
Inspection method: Remove the spark plug to observe the electrode status (ablation, carbon deposits, oil stains).
OBD detection: read the misfire fault code
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Nickel alloy: 20,000-30,000 kilometers
Single platinum: 50,000-60,000 kilometers
Double platinum/iridium: 80,000-100,000 kilometers
Double iridium: 100,000-120,000 kilometers (turbocharged/direct injection engines are recommended to shorten by 10,000-20,000 kilometers)
Chemical cleaning: soak in a special cleaning agent + clean with a soft brush.
Physical cleaning: ultrasonic cleaning or light grinding of the electrode with fine sandpaper.
Emergency treatment: Drive at high speed (3000-4000rpm) for 10 minutes to burn away carbon deposits.
Heat value: The heat dissipation capacity of the spark plug. The larger the number, the faster the heat dissipation (cold type), and the smaller the number, the slower the heat dissipation (hot type).
Impact of choosing the wrong one:
Heat value is too high (cold type): carbon deposits are easy to form at low temperatures, and cold start is difficult.
Heat value is too low (hot type): electrodes are easy to burn at high temperatures, and even detonation occurs.
Usually 20-30N·m (refer to the vehicle model manual for details). Over-tightening will cause the ceramic body to crack, and over-tightening may cause air leakage.
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